rabbitmq cannot start after change config file

rabbitmq runs well, but cannot start after I change its config file according to the official doc.

I install openstack on opensuse13.2, following this doc:

http://docs.openstack.org/juno/install-guide/install/zypper/content/index.html

When reaching at 'Messaging server' section of 'Chapter 2. Basic environment`':

http://docs.openstack.org/juno/install-guide/install/zypper/content/ch_basic_environment.html#basics-messaging-server

Right here,some quote of this doc:

    3. For RabbitMQ version 3.3.0 or newer, you must enable remote access for the guest account.

        Check the RabbitMQ version:

   A.     # rabbitmqctl status | grep rabbit
        Status of node 'rabbit@controller' ...
         {running_applications,[{rabbit,"RabbitMQ","3.4.2"},

   B.   If necessary, edit the /etc/rabbitmq/rabbitmq.config file and configure loopback_users to reference an empty list:

        [{rabbit, [{loopback_users, []}]}].
   C. Restart the message broker service:
    On openSUSE:

    # systemctl restart rabbitmq-server.service

And I proceed like this:

a. controller:~ # rabbitmqctl status | grep rabbit
Status of node rabbit@controller ...
 {running_applications,[{rabbit,"RabbitMQ","3.3.5"},

b.change config file:/etc/rabbitmq/rabbitmq.config,i.e. uncomment this line

%% {loopback_users, []},

c.controller:~ # systemctl start rabbitmq-server.service 
Job for rabbitmq-server.service failed. See "systemctl status rabbitmq-server.service" and "journalctl -xn" for details.

d.controller:~ # systemctl status rabbitmq-server.service
rabbitmq-server.service - RabbitMQ broker
   Loaded: loaded (/usr/lib/systemd/system/rabbitmq-server.service; enabled)
   Active: failed (Result: exit-code) since 二 2015-04-14 14:27:59 CST; 30s ago
  Process: 7387 ExecStopPost=/usr/bin/rm /var/run/rabbitmq/pid (code=exited, status=0/SUCCESS)
  Process: 7345 ExecStop=/usr/sbin/rabbitmqctl stop (code=exited, status=2)
  Process: 7219 ExecStartPost=/usr/sbin/rabbitmqctl wait /var/run/rabbitmq/pid (code=exited, status=2)
  Process: 7218 ExecStart=/usr/sbin/rabbitmq-server (code=exited, status=1/FAILURE)
 Main PID: 7218 (code=exited, status=1/FAILURE)

4月 14 14:27:59 controller rabbitmqctl[7345]: attempted to contact: [rabbit@controller]
4月 14 14:27:59 controller rabbitmqctl[7345]: rabbit@controller:
4月 14 14:27:59 controller rabbitmqctl[7345]: * connected to epmd (port 4369) on controller
4月 14 14:27:59 controller rabbitmqctl[7345]: * epmd reports: node 'rabbit' not running at all
4月 14 14:27:59 controller rabbitmqctl[7345]: no other nodes on controller
4月 14 14:27:59 controller rabbitmqctl[7345]: * suggestion: start the node
4月 14 14:27:59 controller rabbitmqctl[7345]: current node details:
4月 14 14:27:59 controller rabbitmqctl[7345]: - node name: rabbitmqctl7354@controller
4月 14 14:27:59 controller rabbitmqctl[7345]: - home dir: /var/lib/rabbitmq
4月 14 14:27:59 controller rabbitmqctl[7345]: - cookie hash: kBnKPRMCXBnfQlB8kipSdA==